While treatment can reduce substance use and related problems, most clients cycle through periods of recovery and relapse after discharge. Continuing care services have been shown to help youth maintain therapeutic gains and improve long-term outcomes, but they can be expensive to implement and are often not reimbursable for treatment programs. The proposed work builds on findings from adult studies and limited research with youth that have demonstrated the efficacy of delivering continuing care services by telephone. We propose to randomly assign 400 adolescents at discharge from residential treatment for alcohol and other drug use disorders to either usual continuing care (UCC) or UCC plus Volunteer Telephone Continuing Care (VTCC). UCC consists of referrals to outpatient services and mutual aid support groups in a youth's home community and are typically not initiated (Donovan, 1998; Godley & Godley, 2011). VTCC is delivered by volunteers who initiate and maintain a schedule of supportive contact through telecommunication for 9 months post-discharge. The VTCC protocol includes a subset of procedures from the Adolescent Community Reinforcement Approach (A-CRA; Godley et al., 2001), including increasing pro-social behavior (involvement with pro-recovery peers and activities), goal setting, and client-directed homework. All participants will be assessed at intake into residential treatment, discharge, and at 3, 6, 9, and 12 months post-discharge. Data sources include standardized interviews, urine tests, and project records. The aims of this study are to: 1) evaluate the main effect of VTCC on changes over time on improving pro-recovery peers and activities, decreasing alcohol and other drug (AOD) frequency of use, and AOD-related problems during the 12 months post-discharge; 2) evaluate the extent to which changes in pro-recovery peers and activities mediate the effects of VTCC on changes in AOD use and AOD-related problems over 12 months; and 3) evaluate the extent to which treatment readiness moderates the main effects of VTCC on changes in pro-recovery peers and activities, AOD frequency of use, and AOD-related problems at month 12. If proven effective, the use of volunteers will provide a new and potentially low-cost method for treatment programs to implement post- treatment support for adolescents and maintain continuing care services over the extended treatment time period recommended by McKay (2005; 2009).